## ADDED Requirements

### Requirement: API test project exists

An xUnit test project SHALL exist at `tests/ChatAgent.Api.Tests/` targeting the API project, with xUnit, Moq, and Microsoft.AspNetCore.Mvc.Testing as dependencies.

#### Scenario: API tests run

- **WHEN** `dotnet test` is run from the solution root
- **THEN** API tests are discovered and executed

### Requirement: Client test project exists

An xUnit test project SHALL exist at `tests/ChatAgent.Client.Tests/` targeting the Client services, with xUnit and Moq as dependencies.

#### Scenario: Client tests run

- **WHEN** `dotnet test` is run from the solution root
- **THEN** Client service tests are discovered and executed

### Requirement: HealthController test coverage

Tests SHALL verify that GET /api/health returns HTTP 200 with a valid HealthResponse containing a non-empty Status and a recent Timestamp.

#### Scenario: Health endpoint returns 200

- **WHEN** a GET request is sent to /api/health
- **THEN** the response status is 200 and the body contains `status: "healthy"` and a UTC timestamp

### Requirement: ChatController test coverage

Tests SHALL verify that POST /api/chat returns a streaming SSE response containing text deltas and a [DONE] terminator. Tests SHALL mock the upstream Responses API.

#### Scenario: Chat streams text deltas

- **WHEN** a POST is sent to /api/chat with a valid ChatRequest
- **THEN** the response is `text/event-stream` containing `data: {"text":"..."}` events followed by `data: [DONE]`

#### Scenario: Chat handles upstream error

- **WHEN** the Responses API is unreachable or returns an error
- **THEN** the response contains a `data: {"error":"..."}` event followed by `data: [DONE]`

### Requirement: ChatApiClient test coverage

Tests SHALL verify that SendChatStreamingAsync correctly parses SSE events from the backend into text deltas, handles [DONE], and throws on error events.

#### Scenario: Client parses text deltas

- **WHEN** the backend returns SSE events with text deltas
- **THEN** SendChatStreamingAsync yields each text fragment in order

#### Scenario: Client handles error event

- **WHEN** the backend returns an error SSE event
- **THEN** SendChatStreamingAsync throws HttpRequestException with the error message